1. Field of the Invention
The present disclosure relates to a tire tread for a civil engineering vehicle such as a dumper and more particularly to certain elements of the tread pattern of such a tread.
2. Related Art
The working of mines requires recourse to the use of suitable vehicles notably able to carry very heavy loads of the materials processed in these mines, covering longer or shorter distances over ground with some degree of slope and often covered with bodies that may impair grip performance either in terms of traction or in terms of braking or even in terms of steering. These vehicles with a high material bearing capability are fitted with tires of suitable size and capacity to allow very large quantities of materials to be moved around. These tires are of very large dimensions, notably far bigger than the tires intended for heavy goods vehicles.
Each of these tires is provided with a tread having a large thickness (at least 60 mm) of wearable material. Furthermore, this tread is provided with a tread pattern made up of cavities such as grooves and sipes that generate both cavity parts capable of collecting material or water as that part of the tire enters the contact patch during running, and corner edges which are useful in meeting the requirements in terms of grip, whether this be in terms of traction or in terms of braking or even in terms of cornering.
The constraints on the use of the vehicles are such that it is common practice to fit new tires to the front axle of such vehicles and remove them and fit them to the rear axle in order to finish wearing away their tread. The changeover is generally performed when the tread wear is equal to or close to one third of the wearable thickness of material.
It is also known practice to form cavities or voids in order to allow the more solid and thick parts such as the edges axially on the outside of the tread to cool. These cavities are generally open either laterally to the tread or onto the tread surface.
The applicant companies have set themselves the objective of optimizing the design of tread pattern for a tire of this type of vehicle subject to the constraint of changing its location on the vehicle during the life of the tire while at the same time enjoying the benefit of the effect of cooling the solid parts through the use of improved cavities.
Definitions:
In this document, a radial direction means a direction perpendicular to the axis of rotation of the tire (this direction corresponds to the direction of the thickness of the tread).
A transverse or axial direction means a direction parallel to the axis of rotation of the tire.
A circumferential direction means a direction tangential to any circle centered on the axis of rotation. This direction is perpendicular both to the axial direction and to a radial direction.
An equatorial mid plane is a plane perpendicular to the axis of rotation and passing through the points on the tire that are radially furthest from the said axis. In the case of a tread, this plane divides the tread across its width into two halves of equal width.
A rib is a raised element formed on a tread, this element extending in the circumferential direction and making a circuit of the tire. A rib comprises two lateral walls at a contact face, the latter being intended to come into contact with the roadway during running.
A block is a raised element formed on a tread, this element being delimited by circumferentially oriented grooves and transversely oriented grooves. A block comprises more than two lateral walls and a contact face.
A cut generically denotes either a groove or a sipe and corresponds to the space delimited by walls of material that face one another and are distant from one another from a non-zero distance (referred to as the “width of the cut”). It is precisely this distance that differentiates a sipe from a groove; in the case of a sipe, this distance is suited to allowing the opposite walls delimiting the said sipe to come at least partially into contact when that part of the tire is in the contact patch in which the tire is in contact with the roadway. In the case of a groove, the walls of this groove cannot come into contact with one another under normal running conditions.
A tread has a maximum thickness EMU of material that can be worn away during running; once this thickness has been achieved, the tire needs to be replaced by another new tire.
A cavity is a void volume formed in a raised element of a tread. This cavity is delimited, on the contact face of the raised element, by a corner edge forming a contour that is closed on itself or by a plurality of corner edges forming a closed contour.